Remote control system



Fell 26, 1946- H. v. ALEXANDERSSON r-:T AL, 2,395,708

n REMOTE CONTROL SYSTEM Filed May 8. 1940 4 Sheets-Shee 1 ll i in i NQ l-vwx l uw l LMi L 'LH A"E`TORNEY y Feb. 26, H. V. LEXNDERSSN ET ALREMOTE CONTROL SYSTEM 4 Sheets'heet 2 Filed May 8. 1940 NvENTORs HmmmWwf/ww mfm/mfsow ATTORNEY Feb- 25? 1946 H. V. ALEXANDERSSON ET AL2,395,708

REMOTE CONTROL SYSTEM Filed May 8, 1940 4 Sheets-Sheet 3 M //M ATTORNEYFeb. 26, 194:6a H. v. ALEXANDERSSON ET AL 2,395,708

REMOTE CONTROL SYSTEM Filed May 8, 1940 4 Sheets-Sheet 4 Vx y PatentedFeb. 26, 1946 REMOTE CONTROL SYSTEM Harald Valdemar Alexandersson andCarl-Erik Granqvist, Stockholm, Sweden, assignors to Aga-Baltic RadioAktiebolag,

Stockholm,

Sweden, a corporation of Sweden Application May 8, 1940, Serial No.333,926

' In Sweden May 24, 1939 14 Claims.

In remote control systems of the variable frequency type in which thetransmitted frequency isa function of the position of an object at thetransmitter, and in which the receiver contains a frequency-meter orother similar device which takes a position dependent upon the receivedfrequency, there is diiliculty in obtaining suicient precision,particularly in cases where a large angular movement is to betransmitted. In remote control systems of this type, the object at thetransmitter, the angular movement of which is to be reproduced at aremote posi- I tion, is connected toa means to control the frequencytransmitted which may, for example, be a frequency of the order of radiofrequencies.

The receiver is provided withmeans selective for frequencies ofdifferent ranges, which, in the simplest case, may constitutefrequencymeters An improved form of receiver includes an scillatortogether with a tuning circuit the tuning means of which is controlledby a motor which also drives the controlled object. A discriminator isprovided for comparing the received frequency with the oscillatorfrequency generated in the receiver and the motor is connected to tunethe oscillator frequency to a value which is a function of the receivedfrequency.

As frequency determining means, simple oscillation circuits may be used.However, these have only a limited frequency range which must cover theentire range of movement of the transmitter object. On the other hand,the precision of the system is determined by the frequencydiscriminating power of the receiver, which cannot be made too sharpwithout risk of overcontrol and hunting and without risk that the lcontrol Will be unable to follow if there is too great a lag between thetransmitter and the receiver. Hence, the precision is reduced as therange of movement of the transmitter object increases.

Within certain fields, especially within the artillery art, it may benecessary to transmit angles up to 360, or even up to a multiple of 360with high precision. In such cases the precision usually becomes toosmall. The precision can be increased, however, by causing the receiverobject to rotate a plurality of times, but this involves certaindisadvantages which make such an arrangement impractical. Assume forinstance, that the receiver organ is a standard frequency-meter. During360 rotation of the transmitter object the frequency-meter will,provided it is ,used in the best possible way, sweep over its entirescale. If the transmitter object rotates a further 360, therebyrepeating the same frequencies, the frequency-meter must again bebrought into its initial position, a problem which is rather difficultto solve, if the frequencymeter is also used as driving means for thereceiver object. During the overlapping movement in question there issuch unreliability in the coincidence between the transmitter and thereceiver, that the operation of the receiver may be very inaccurate.

Furthermore, there is also a risk of error in that it is never certainthat the transmitter object and the receiver object have passed throughthe same number of revolutions. If, for example, the receiver, for somereason, should become uncoupled while the transmitter rotates one ormore turns, the receiver would, when again coupled in, show the correctangular position, but would not have made the correct number of turnsand there would be no possibility of supervision unless the receiverwereI provided with an indicator to show the number of turns from itsinitial position.

The present invention relates to an arrangement for overcoming the abovedisadvantages. In accordance with the present invention the transmitteris arranged so as to sweep over a plurality of different frequencyranges, for instance, two frequency ranges which are separated from eachother. In this way a more accurate and continuous control is maintained.The transmitter may include units responsive to the two frequency rangeswhich are operated respectively over alternate half revolutions of thetransmitter object or the two units may operate simultaneously for fineadjustment and coarse adjustment respectively. In the latter Case the neadjustment unit will be connected to have a greater range of movementthan the coarse adjustment unit.

In the following the invention is described with reference to theannexed drawings, in which Fig. 1 is a wiring diagram of a completeremote control arrangement according to the invention, Fig. 2 is adiagram for explanation of the operation of the arrangement according toFig. 1, Fig. 3 is a wiring diagram of a modified form of thetransmitter,Fig. 4 is a diagram, corresponding to the diagram of Fig. 2, forexplanation of the operation of the transmitter of Fig. 3, and Fig. 5shows diagrammatically a receiver to be used with the transmitter ofFig. 3.

The transmitter according to Fig. 1 contains two transmitting units S1and Sz for transmitting radio frequency within different frequencyranges. The tuning means for controlling the frequency of each of thetransmitting units includes condensers C1 and C2, respectively. 'I'hetwo condensers are mounted on the same shaft as the transmitter object.The shaft also carries a cam 2 of a switch X, which includes a contactspring I, arranged to be brought, by the cam 2, alternatively in contactwith one or the other of two contacts 3 and I. During the rotation ofthe shaft, therefore, the contacts I--3 and the contacts I-I arealternately closed to connect the condenser C1 and the condenser C2alternately into the oscillation circuits of the transmitters S1 and S2.

As will be apparent from the following explanation of the operation ofthe system, it is advantageous, if the Contact arrangement is so madethat one of the contacts is closed immediately before the other isopened and vice versa, so that the closing of the contacts will alwaysoverlap for a short time.

The two transmitting units S1 and S2 are connected in parallel by acommon line L to the receiver, which consists of two superheterodyneunits M1 and M2, so arranged that one of the receiver units M1 has thesame frequency range as one of the transmitting units S1, and the otherof the receiving units M2 has the Asame frequency range as the othertransmitting unit S2. The receiving units are only schematically shown,as their construction has nothing to do with the present invention.Concerning the arrangement and operation of the receiver it is believedto be suiiicient to mention the following:

Each of the receivers contains an oscillator, the tuning condensers ofwhich C1111 and C1112, respectively, are arranged on a common shaft,which also serves as the shaft of the controlled object. The controlmotor m is arranged on this same shaft. This motor is provided with twofield windings, wound in such a way that the motor develops torque inone direction under the iniiuence of one of the field windings and inthe opposite direction under the influence of the other field winding.

In the intermediate frequency channel of each of the receiving units isarranged a frequency discriminator D1 and D2, respectively, of somesuitable kind, which after rectifying the intermediate frequency,creates voltages which are a function of the displacement of thefrequency in the intermediate frequency channel from the frequency towhich the channel is tuned. Thus each of the discriminators contains tworectiiiers L11 and L12 and L21 and L22, respectively The direct currentvoltages, obtained from the rectifiers, are amplified by means of theamplifier valves R11, R12, R21 and R22, the valves R11 and R21 beingconnected in parallel to one of the field windings of the motor m andthe two other of the amplifier valves being connected to the other ofthe two windings.

Due to the above described coupling arrangement, the superheterodynereceiving units, will convert the frequency received from thetransmitting unit into an immediate frequency, preferably equal to thedifference between the signal frequency of the transmitting unit and-the internal oscillator frequency of the receiver, although the sum maybe used. If theinternal oscillatory frequency is correctly tuned, afrequency difference will be obtained which is exactly the same as thetuning frequency of the intermediate frequency channel, but if theoscillator frequency is wrong the intermediate frequency will bedisplaced in one direction or the other. Dependent upon the direction inwhich the intermediate frequency is displaced, there is obtained astronger field current through one of the two field windings of themotor m. which causes the motor to rotate, and to turn the condensers ofthe receiver units in a direction to bring the intermediate frequency tothe correct value where both of the fields in the motor are again inbalance and the motor stops.'

The operation of the arrangement as a whole is as follows:

It is assumed that the transmitting unit of the system is initially inthe position shown in Fig. 1. The movement is further assumed to takeplace `in clock-wise-direction. As apparent from the drawing thisrotation of the cam closes the contacts l-3 of the switch X and thecondenser C1 is coupled in, the transmitter unit S1 therefortransmitting a frequency which varies with the position of the condenserduring the rotational movement. The condenser is cut so that thecapacity decreases when turned in clock-wise-direction, and therefor thefrequency will increase, as shown in Fig. 2 by the curve a-b. Thisincrease of frequency continues during a half revolution, and then theswitch X uncouples the condenser C1 and couples in the condenser C2, sothat the transmitting unit S2 begins to operate. The transmitting unitS2 transmits within a frequency band different from that of thetransmitting unit S1. Its frequency thus will vary in the manner shownby the curve c-d in Fig. 2, until after a further half revolution thetransmitting unit S2 is uncoupled and the transmitting unit S1 is againcoupled in.

If the movement takes place very slowly, there is a possibility that themotor M may not start immediately upon switching between the twotransmitting units. This may be avoided if, as mentioned above, theoperation of both of the transmitting units is made to overlap during ashort interval.

The receiver units are provided with condensers C1111 and C1112,respectively, which are cut in such a way that they produce the correctintermediate frequency when the controlled object is in the sameposition as the transmitter object. The receiver condenser C1111corresponds to the condenser C1 of the transmitter unit S1, and thereceiver condenser C1112 corresponds to the condenser C2 of thetransmitter unit S2. Due to the above described operation of thereceiver object the receiver will therefor always assume the sameposition as the transmitter object,

In order to vary the receiver frequency the usual methods for frequencycalibration, known in the radio art may be used. A very much greaterprecision may, however, be obtained, if the condenser of the transmitterunit as well as of the receiver unit is designed to cover a greatercontrol angle than e. g. as shown in the figure, 270, the condensersbeing made to give a logarithmic frequency variation with the angle ofrotation, at least within the range which is used.

One can then always choose an angle of 180 for the transmittingcondensers and a different angle for the receiver condensers, at whichthe above mentioned frequency relation is present. In this way a simplecondenser of the same shape is obtained for the transmitter as well asfor the receiver while maintaining an accurate alignment between theangles of rotation of the transmitter and of the receiver.

It is easy to prove mathematically, that in this asaavos is subordinatedunder this main movement, the

last mentioned movement being here supposed to be a vernier movement.'I'he shaft of the transmitter object is referred to as I0. This shaftmay for instance be connected to some indicator which may be read in aremote place. Such an indicator is schematically shown at II. On theshaft I there is arranged aworm gearing I2, by which the shaft I0 isconnected to another shaft I3 in a gear ratio of 100:1, the last namedshaft determining the main movement. The shaft I0 carries a rotor I4 ofa double condenser, having double stators I and I6. Thus one condenseris formed between the rotor I4 and the stator I5, whereas anothercondenser is formed between the rotor I4 and the stator I6. A :cam wheelIl, carried by the shaft I0, causes a contact spring I8 to be in contactwith the contact point I9 during substantially half of a revolution ofthe cam I1 and with the contact point 2li during substantially the oherhalf of its revolution.

'I'he shaft III is grounded, so that the condenser I4-I5 is permanentlycoupled in parallel to the coil 2I of an oscillator valve 22, and thecondenser I4-I5 is in a corresponding manner pennanently coupled inparallel with the coil 23 of a second oscillator valve 24. Theoscillation circuit, formed by the coil 2| and the condenser I4-I5 may,however, be short-circuited by means of the contacts I3-I9 and in acorresponding way the oscillation circuit of condenser I4-I6 and coil 23may be short-circuited by contacts I8-2II. The anode circuits of theoscillator valves 22 and 24 are vinductively coupled to the transmissionline 25.

The shaft I3 carries a further condenser, lncluding a rotor 26 and astator 2l. This condenser is coupled in parallel to the coil 23 of anoscillator valve 29, the anode circuit of which is also connectedinductively to the transmission line 25.

For explanation of the operation of the transmitter, reference is madeto Fig. 4. It is assumed that the shaft I0 turns a plurality ofrevolutions in clock-wise direction. Due to its rotation the capacityI4-I 5 will initially increase, so that the frequency 0f the oscillator22 decreases successively. The oscillation circit 0f oscillator 24 isshort-circuited by the contacts I3 and 20. At the same time also shaftI3 turns, but due to the gearing this takes place in counter-clockwisedirection and also at a speed which is assumed to be only one hundredthof the speed of rotation of shaft III. The capacity of condenser 26--21will therefor successively decrease, and the created frequency willincrease. When shaft I0 has turned half a revolution, the short-circuitof condenser I4-I6 is opened, so that the oscillator 24 becomes active,and a moment later the oscillation circuit of oscillator 22 becomesshort-circuited, this oscillator thereby becoming inactive.

' After a further half revolution condenser 22 becomes again active, andoscillator 24 is put out of action.

The oscillators 22 and 24 have similar condensers. because of the factthat the condensers have a common rotor. Also the coils 2I and 23 aresimilar. 'I'he frequencies therefore will vary in the manner shown inFig. 4. The line 30, drawn in full, represents the frequency ofoscillator 29, and the line 3I represents the frequency of oscillator 22and the line 32 represents the frequency of oscillator 24. Parts of thelines 3| and 32, which are drawn in full, represent operating periods ofthe respective oscillators, whereas the broken parts of these linesrepresent the time while the oscillation circuits of the oscillators areshort-circuited.

The receiver for the transmitter of Fig. 3 is, shown in Fig. 5` Thetransmission line is also here designated as 25. It is inductivelycoupled through a transformer 33 to the receiver for the main signal andalso through two transformers 34 and 35 to each of two cooperatingreceivers for receiving the Vernier signal. The main signal receiverconsists of an oscillator valve 35 connected in a standard manner tooperate as a combined oscillator and modulator. nections for this valveare here of no importance except as far as this valve converts the mainsignal frequency to a frequency corresponding to the difference betweenthe main signal frequency and the oscillator frequency, such as theintermediate frequency in a superheterodyne receiver. The transmitterfrequency may have a range of 15G-200 kcs. and the receiver oscillatorfrequency a range of 250-300 kcs., producing an intermediate frequency100 kcs. Of course the invention could also be used according to theinfraheterodyne principle, although it has not been found asadvantageous The oscillator circuit `of the oscillator valve 36 containsthe coil 31, coupled in parallel with a trimmer condenser 38 and thetuning condenser 33. Condenser 39, which is thus the main tuningcondenser, is mounted on the same shaft as the The anode circuit of theoscillator valve con-l tains a circuit tuned to the exact value of theintermediate frequency and containing th'e condenser 43 and the coil 44.Coil 44 is inductively coupled to a second coil 45, tuned by means ofcondenser 46.' Further the coils 44 and 45 are connected to each otherby means of a condenser 41, which is connected between the mid-point ofone of the coils, for instance, coil 45, and the high potential end withreference' to alternating current of th'e other coil, in this case thecoil 44. This coupling arrangement is sharply tuned and is known per se.It operates in the following manner:

The voltage of a tuned primary circuit and in a tuned secondary circuitare normally displaced in phase by 90. If the primary voltage is added,as by the condenser 41, to one half of the secondary voltage in positivedirection and to the other half of the secondary voltage in negativedirection, due to the symmetry between these two voltages the resultingvectors will be exactly equal. If the frequency differs from that towhich the circuits are tuned, however, the symmetry is destroyed. Ofcourse the two half voltage vectors The conforman acute angle with theprimary voltage vector, whereas the other one forms an obtuse angle. Theformer resultant will thereby be essentially greater than the latterone, and if both of the voltages are rectified different direct currentvoltages will be obtained.

'I'he rectifiers, in which the rectification is made, are in the figureshown as valves 48 and 49, which work on the load resistors 50 and 5|,respectively. The voltages across the respective load resistors are fedeach to one of two direct current amplifier valves 52 and 53, the anodecircuits of which are connected each to one of the field windings 54 and55 of th'e motor 4 The coupling arrangement for Vernier reception isarranged in substantially the same manner as the main receiving system.The only difference is that two cooperating receivers are provided, cneof which responds to the frequency 3| and the other to the frequency 32in Fig. 4. In order to simplify the description the same referencenumerals have been used in the Vernier receivers as in the mainreceiver, said reference numerals having been increased by one hundredfor one of the Vernier receivers and by two hundred for the other.

The two receiver units are provided with condensers with a common rotor58, mounted on the common control shaft 56, which' is driven by motor51. The shaft 56 actuates the receiver object 59, which is shown as aVernier dial. The anode circuits of the direct current amplifier valves|52 and 252 are connected together and connected to supply field currentto the field winding 60 of motor 51, whereas the direct current ampliervalves |53 and 253 are connected together to supply field current to thefield winding 6|.

The operation of the arrangement is the following:

When shaft IU in Fig. 3 turns, it causes the transmission of twodifferent frequencies, indicated by the curves 3| and 32 of Fig. 4,which vary as a function of the angular position of the shaft I0.Another frequency is transmitted by oscillator 29 in the form indicatedby the curve 30 in Fig. 4, which is a function of the angular positionof the shaft I3. For each half revolution of the sh'aft l0 a fullfrequency range, corresponding to the capacity variation during 180 ofthe condenser |4-I5 and |4--|6, respectively, is run through by thetransmitter units 22 and`24, as shown in Fig. 4 by curves 3| and 32respectively.

On the receiver side the frequency 3D is received by means of thetransformer 33 of the main receiver, in which it is modulated with thefrequency created by oscillator valve 36, so that an intermediatefrequency is formed. vIf it now should happen that this intermediatefrequency agrees with the frequency to which the discriminator 43-46 istuned, the reception of th'e frequency 30 does not result per se in theoperation of the motor 4| of the receiver. If, however, the frequencydiffers from the above, a stronger magnetizing current is obtainedthrough one of the windings 54 and 55 of the motor 4|, which causes th'emotor to operate and the shaft 40 is tuned, until condenser 39 hasreached such a position that the correct frequency is restored in theintermediate frequency channel of the main receiver. The dial 42 thenwill take the position corresponding to that of the main transmitter,but which according to the suppositions may not have sufficientprecision.

At the same time as the frequency 30, Fig. 4, is transmitted,transmission of a further frequency 3| or 32 from the Verniertransmitter takes place. This is received by means of the receiverswhich contain oscillator valves |36 and 233, respectively. As a matterof fact, the frequency is received by both of these receivers, but onlyone of them is in the position to operate. Assume, for instance, thatthe main receiver has been roughly positioned so that the oscillator |35operates, then due to the characteristic of the discriminators of thistype a substantial voltage difference may be obtained between the directcurrent voltages created by rectifiers |43 and |43 if th'e shaft 56 isnot correctly positioned. This direct current voltage differenceinfluences the field windings of motor 51, so that an automaticcorrection is obtained.

Meantime, howeverl the oscillator 235 produces an intermediate frequencywith the incoming frequency, but this differs widely from theintermediate frequency to which the discriminator is tuned. Sincediscriminators of this kind produce very small or no current deviation,when th'e frequency is widely displaced from the dscriminator frequency,the result is that about equally strong field currents are delivered bythe amplifier Valves 252 and 253 to windings 50 and 6|1 said currentsalso being substantially weaker than the currents delivered by Valves|52 and |53. The fact that the oscillator 236 is allowed to operate atthe same time as oscillator |36 therefore does not cause any appreciabledisadvantage.

If necessary, a contact arrangement (not shown) may be provided on shaft55, by means of which the field windings 50 and 6| are connected in turnto the valves |52 and |53 and to the valves 252 and 253.

When the system has been out of operation, one can not with certaintyassume that the transmitter and receiver are in agreement. It thus mayhappen that the receiver or the transmitter has meantime changed itsposition, so that a difference in position of half a revolution of shaftI0 or a multiple of such' a half revolution has occurred. In order toprevent this, the motor 4| may be made strong enough in relation to themotor 51 to always secure correct rough adjustment within a range oftolerance which is less than plus or minus a quarter of a revolution ofthe shaft I0, or the motor 51 may be cut oi! until the motor 4| hascompleted control within the said tolerance. This may be done byconnecting the field windings 54 and 55 of motor 4| in series throughthe windings 62 and 63 of a differential relay 65 having a contact 64.At certain differences between the currents through' said windings 62and 63 the contact 54 of the relay opens the armature circuit of motor51, which is not closed until the difference between the two currentshave decreased to a sufficiently low value.

Of course it is possible to utilize additional stages of Vernieradjustment to obtain a still more exact adjustment. In this manner it ispossible to obtain a precision in the remote control which is onlylimited by the mechanical precision of the gearing. If the invention isused to control with high precision the position or direction of someobject, for instance, a piece of ordnance, the control mechanism of thepiece may be connected with the shaft 56 as indicated by th'e dial 59.

What we claim is:

`1. In a remote control apparatus, a transmitter including a pair ofunits each having means for producing and transmitting signals havingfrequencies variable over a predetermined range and including a controlmember to control as a function of its position the frequency of saidsignal, and a receiver, including a controlled object, and a pair ofunits tuned for receiving the signals transmitted from said first units,said last units each having means responsive to variations in thefrequency of the received signal from the frequency to which said lastunits are tuned for effecting a control of said object corresponding tothe movement of said control member, said control member being connectedto cause said first units to alternately transmit signals sweeping overtheir respective ranges, whereby said controlled object is controlledalternately by the receiver units cf said pair.

2. An apparatus as defined in claim 1 including a tuning circuit foreach of said units of said pair, and a variable condenser having twostators and a common rotor, one of said stators being includedin thetuning circuit of one of said pair of units and the other stator beingincluded in the n ,ter including a pair of units having means forproducing and transmitting signals having frequencies variable over apredetermined range and including a control member to control as afunction of its position the frequency of said signals, and a receiver,including a controlled object, and a pair of units tuned for receivingthe signals transmitted from said rst units, said last units each havingmeans responsive to variations in the frequency of the received signalsfrom the frequency to which said last units are tuned for effecting acontrol of said object corresponding to th'e movement of said controlmember, said control member being connected to cause the frequency ofone of said signals to vary at a rate substantially greater than that ofthe other of said signals and to cause said rst signal to successivelysweep over its range while said second signal varies progressively andcontinuously in the same direction during a predetermined range inmovement of said control member whereby said first signal may be usedfor effecting ne adjustment of said controlled object and said secondsignal may be used for effecting coarse adiustment thereof.

5. In a remote control apparatus according to claim 4 in which thesignals are respectively intended for fine control and coarse control,rotat-- able tuning means at th'e transmitter and receiver for each ofsaid signals and reducing gears interconnecting the rotatable tuningmeans for the ne and coarse' signals at the transmitter and receiver.

6. In a remote control apparatus according to claim 4 in which thesignals are respectively intended for fine control and coarse control,rotatable tuning means in the respective channels at the receiver, andmotors actuating said tuning means in response to frequency variationsin the received signals, the motor actuating th'e tuning means for thecoarse control being suiiiciently powerful to effect control regardlessof the energization of the fine control motor.

7. In a remote control system according to claim 4 in which the signalsare respectively intended for fine and coarse control, control meansresponsive to each of said signals and means rendering the fine controlmeans ineffective ,until the approximately correct coarse control iseffected by the coarse control means.

8. In a remote control system according to claim 4, tuning means for thecontrol channels including variable condensers having logarithmiccapacity characteristics.

9. In a remote control system according to claim 4, tuning means for thecontrol channels including variable condensers having logarithmiccapacity characteristics, the, condensers of the respective channelsbeing angularly displaced relative to each other.

10. In a remote control apparatus, a transmitter including a unit havingmeans for producing and transmitting a signal having a frequencyvariable over a given range anda pair of units having means forproducing and transmitting signals having frequencies variable overdifferent ranges and including a contro1 member to control, as afunction of its position, the frequencies of said signals within therespective ranges, and a receiver, including a controlled object, a unittuned for receiving the first-mentioned signal and having meansresponsive to variations in vthe frequency of said rst signal from thefrequency which said unit is tuned to receive for effecting control ofsaid controlled object, and a pair of units each tuned for receivingsaid second mentioned signals, and having means responsive to variationsin the frequency of said last signals from the frequency which saidunits are tuned to receive for modifying the control of said object.

11. An apparatus as dened in claim 10 in 12. In an apparatus as definedin claim 10.-

means alternately rendering the units ofl said pair operative, saidmeans being connected to said control member to cause the signals fromsaid last units to alternately sweep over their respective ranges inresponse to continued movement of said control member.

13. In an apparatus as defined in claim 10, means alternately renderingthe units of said pair operative, said means being connected to saidcontrol member to cause the signals from said last units to alternatelysweep over their respective ranges in response to continued movement ofsaid control member, said last means causing the periods of energizationof the respective units of the pair of transmittir g units to overlapwhereby continuous control is effected thereby.

14. An apparatus as defined in claim 10 i which said second mentionedsignals are variable over the same range as each other, but over adifferent range from that of the first mentioned signal.

HARALD VALDEMAR ALEXANDERSSON.

CARL-ERIK GRANQVIST.

